Being one of the shorter texts on Archive.org dealing in this topic, I decided on spur of the moment to read this one.
The author's struck a good compromise between thoroughness & succinctness.
It's this kind of guidance that I think the young men of this country are severely lacking. A fair amount of the crime & mental health crises in this country might be prevented if people were still inculcated in this kind of thing.
Rather interesting the author's comments on Page 4 & 5 that the ability to persistently display gentlemanliness is an inheritted trait. One would struggle to get away with saying things of the like today.
The author's discussion of the distinction between honesty & honour is interesting. At first it may seem a superfluous section, but reading it through to the end I can see why these non-identical twin morals would need to be explained in contrast to the other. Misidentifying which of the two ought to take precedence over the other in a given circumstance is probably one of the main catalysts in causing disputes between men since before recorded history.
One area in the general discussion of gentlemanliness I found particularly interesting was on Pages 25 & 26 on confidentiality being the default in conversation between two parties. 1866 apparently was an era in which privacy was valued over gossip - very different from today.
The comment on Page 27 that a gentleman should avert his eyes when a woman is coming towards him down a staircase so as to avoid viewing her ankles amused me, given how much women's fashion has evolved in a century and a half. When weather permits, women in this country commonly expose not only their ankles, but their legs right up to half their thighs, & their arms too. I've experienced more than once women bending themselves forward to reveal their busts to me. But folks in 1866... they fretted about strange men seeing women's ankles.
On the topic of women and lastly, I found the author's description of how a gentleman should view women to be flowery, saccharine, even quixotic. It may have been applicable for knights in the Medieval era & maybe even in the Victorian Era, but it certainly isn't relevant in this country in the 21st century.